Velocity modulation devices



SePt- 6, 1955 E. TouRAToN ET AL 2,717,327

` VELOCITY MODULATION DEVICES Filed Jan. 15, 1948 HTA msm/VCE man 6 f7 if. il

n l' H lNvENToRs EMILE TOI/@TON CLAUDE ou'HoL/.ssfm/ E Z BY REN WOB/IDA ATTORNEY United States 2,111,321 y VELOCITY MonULATloN DEVICES Emile Touraton, Claude Dumousseau, and Ren Zwobada, Paris, France, assignors to International Standardy Electric Corporation, corporation of Delaware New York, N. Y., a

The present invention relates to tubes. v I

One object of the present invention is a velocit'yfmodulation tube of the reiiex type, in which progressive wave guides are used instead of resonating volumes.

Other objects and features of the present invention will be apparent from the following description of an embodiment made in relation to the drawings in which:

Fig. 1 shows in cross-section a velocity modulation tube incorporating features of the invention.

Fig. 2 is a vertical section taken along the line 2 2 of Figure 1.

Figs. 3 and 4 show curves useful for understanding the operation of the velocity modulation tubes of the present invention, and v Figs. 5 to 7 show other embodiments of the invention.

Referring now to Fig. 1, this figure shows a velocity modulation tube incorporating features of the invention which comprises a wave guide 1 and a wave guide 2 brought to a given potential and through which a at beam of electrons, emitted by an elongated cathode 3, flows in succession. The flat electron beam is reected by the decelerating field produced by a reflector 4 and successively flows through wave guide 2 and wave guide 1 from the reflector, and is finally attracted by the bottom part of guide 1 as shown in Figure 2 by a dotted line.

The dimensions and the potentials of the'various elements are chosen in such a way that the transit time of the electrons in each guide be equal to T/4, T being the period of the oscillation, which varies according to the potential of the reflector. The total value ofthe transit time for both guides is therefore T/2. It is also necessary that the time elapsing between two successive passages of the unmodulated electrons in the centre of guide No. 1 be equal to KT -l-T/4, where K is an integer.

On Fig. 1 the waves travel in the guides from right to left. Wave guide 1 is terminated on the left by a load 6 which must be equal to the characteristic impedance of the guide. Guide 2 is terminated on the right in its characteristic impedance 7. The left end of guide 2 feeds the right end of guide 1 through a connection without reection, in such a way that at two points 8 and 9 of the same vertical section of guides 1 and 2, the wave travelling in guide 1 is lagging one fourth of a period behind the wave travelling in guide 2.

It will be assumed that the electron beam is suitably hunched at its second passage in guide 2 and that the high-frequency potential in the guide is such that the bunches of electrons of the beam be retarded. These bunches of electrons take one quarter of a period to go from guide 2 to guide 1. Since the wave which travels in guide 1 lags one-fourth of a period behind the wave which travels in guide 2, the bunches of electrons are slowed down again in guide 1. The beam will therefore give up energy to guide 2 and then to guide 1 and it is possible to pick up this energy. The time of travel in the two guides is sufficiently' short so that the electrons remain grouped together.

velocity modulation lee Y Fig. 3 shows the high-frequency potentialsA ofvthe guides, the distancefrom the origin of. each guide being given along theabscissa and the high-frequencypoten tials ofi the guidesin the ordinates. -ev The potential zincach point ofguide 1. isequal Vto the sum of the potential prevailing at the right-endof guide'2 plus an additional potential proportional: to .the distance from this point to the beginning of guide 1 (see-Fig. 3 curve-10).

The potential in each point of guide 2 is proportional to the distance from this vpoint-tothe -leftend of the guide (see Fig. 3', curve 1.1). s f y Fig. ,4 shows the high Afrequency potential inboth guides in vectorial form, showing the lag of Vone fourth of a'p'eriod of the potential of guide 1 (shown by vector 12) behind the potential of guide 2 .(shown by vector 13).- :fr-

d `Dur`ing its travelitheelectron beam is frst modulated by the potential of guide 1 and one fourth of a period later it is modulated by the potential of guide 2, which is leading ahead of potential of guide 1 by one fourth of a period. The modulation due to guide 2 is therefore in phase opposition to the modulation due to vguide 1.

The resulting electron modulation is equivalent to a modulation by a single potential, in phase with potential of guide 1 and equal in absolute value to the difference of the absolute values of the potential of guides l and 2. Since this difference is constant for all [the points of the guide, as may be seen on Fig. 3, the electron beam is uniformly modulated on the whole length Tof the guides.

The potential of the reflector is adjusted so that the oscillationfwhich takes place has a given wavelength. In the above-mentioned conditions, if the reflector potential is slightly changed, for instance in such a,l way that the transit time be increased, there will be a drift of the oscillations towards longer wavelengths so that the number of periods included in the transit time of the electrons remain the same. It will thus be possible to vary the 'frequency of oscillation of the tube by a mere change in the'potential of the reflector. This frequency drift may be large, for

. instance ten per cent of the fundamental frequency.

Fig. 5 shows a top view of a velocity modulated tube incorporating features of the invention and Fig. 6 a sectional view along thereof. Inside a glass vessel, two guides 14 and 15 are connected end to end, :'and wound spirally. They have a common wall and are therefore at the same potential, their length is equal to (K4-Mal), l being a value close to the oscillation wavelength of the tube and K an integer.

Cathode 17 and the focussing system 18 of the cathode ray beam are external to the spirals. Reflector 19 is located inside the spiral and its shape is adapted to reflect the beam in a given direction.

With reference to Figure 7 there is shown a velocity L modulation tube incorporating a further embodiment of this invention. Helically wound wave guide of two turns is used in this embodiment. The helically wound wave guide forms two wave guides 20 and 21, one above the other between a cathode 22 and a reector 23 each of which is formed as a single turn of a helix. Y

Although the present invention has been described in relation to embodiments it is clear that these embodiments may be modified without departing from of the invention.

We claim:

l. A high frequency electronic devicecomprising an elongated cathode electrode, an elongated reector electrode whose length runs in substantially the same direction as that of the cathode electrode, said electrodes being spaced apart a given distance throughout their length, wave guide lengths disposed adjacent each other in overlapping relation between said electrodes and spaced the scope y tererom, waive guide .lengths being connected to each.` otherand. having. openings therethrough, substantially co-extensive with said electrodes and in alignment therewith, the transit time of an electron between corresponding points; in. saidopenings being a: quarter of. periodl at the operating lrequ'ency, the; vdistance, between said corresponding pointsi as: measured through the connected wave guide: lengths; beingeffectively elecf treafi-ly aqnarter wavelength at the same frequencyaand means: effectively terminating said waveb guide lengths inI 10 their-characteristic impedance, to. thereby prevent standing'waves.,

2. A high frequency electronic device according to claim 1;, .wherein saidwave guide lengths comprise a continuousvwave guide structure 3. A high frequency electronicdevice accord-ing V to claim 1i, wherein saidl electrodes: and` said wave guide lengthsare circularly disposed.

4c A1 high frequency electronic device according to ela-im, 3, wherein said electrodes and wave guide lengths are disposed substantially in concentric relation.

'-5.- A higlr frequency electronic device according to f claiin 3,*wherein the wave guide lengths comprise parts Qi` a .spirally wqundwave guide, U

6v A high frequency electronic device according to claim 3, wherein the wave guide lengthscornprise parts of a helically wound wave guide.

7. A high frequencyrerlectronic device according to claim 3, wherein said electrodes are disposed in parallel planes, andv the wave guide lengths areldisposed'f between said planes.

References. Cit'edin the flevoiy .Eatent'4 'A UNITED STATES PATENTS I 2,122,538. Potter. l .lukt-5f, 1938 2,153,728 Southworth Apr. 11, 1,939 2,367,295' Llewellyn I Jan.'l6"1`45 2,368,031 Llewellyn Jan. 23, 1945 2,402,184 Samuel June 18, 1946 2,450,026 Tomlin Sept, 28*19'48 2,457,524 Bowen Dec. 28,1343 2,462,087 Fremlin Eeb 2r2 ,l 1249 2,509,374.

. Sunstein ..y f.. May 30, 1950 

